The present invention concerns image pickup tubes, and more particularly it concerns a faceplate structure of the same. Generally, the television camera requires three image pickup tubes, since one image pickup tube is required for obtaining one of three different color signals of green, blue and red. However, there has been developed recently a multi-color image pickup tube or a single tube type color image pickup tube which can take out chrominance signals of two or three colors from one image pickup tube.
In FIGS. 1 and 2 is shown a conventional multi-color image pickup tube wherein over the surface of a faceplate 1 made of light transmitting material such as glass are deposited successively a color separating stripe filter (hereinafter referred to as color separating filter) 2, a thin glass plate 4 via an adhesive 3, a transparent electroconductive film 5, and a photoconductive film 6 to form a faceplate structure 100, the faceplate structure 100 being airtightly secured to one open end of an envelope 10 by a sealing material 7 of indium attached with a signal electrode 8 such that the inside of the envelope 10 is evacuated to vacuum. Light 12 from an object 11 is focused on the photoconductive film 6 via an optical lens 13, thereby forming a charged pattern image corresponding to an image of the object 11 in the photoconductive film 6. An electron beam 14 from an electron gun 9 is focused and scanned on the surface of the photoconductive film 6 by the magnetic field formed by a deflecting coil 15 and a focusing coil 16 arranged around the outer periphery of the envelope 10 to convert the charged pattern into electric current to be taken out from the signal electrode 8 as an electric signal via transparent electroconductive film 5 and indium sealing material 7.
However, in the image pickup tube constructed as above, the faceplate 1 is shaped circular, and there is formed a color separating filter having a correspondingly circular outer periphery on the surface of the faceplate. This necessarily causes waste in material when trying to make a number of filters from out of one sheet of material in the mass production, thereby raising the production cost. Therefore, it has hitherto been proposed to eliminate the waste in the material of the filter by using a color separating filter of a rectangular shape which corresponds to the effective area of the faceplate (normally the rectangular portion at the center of the faceplate). This proposal uses the color separating filter disposed in the vacuum within the envelope 10 and requires this filter to be adaptive for use in vacuum. Thus, both the adhesive and the filter material are limited to the inorganic material, since organic materials are not stable in vacuum as they discharge a great amount of gas. For this reason, it has been extremely difficult to practically manufacture the faceplate structure incorporating the rectangular color separating filter made of the organic material such as prepared by dye method, in spite of the recent remarkable development in the manufacturing technology for color separating filters of organic material.